The perception of shape is essential for object identification and visually guided action. The neural represenation of shape is mediated by a hierarchical system of brain areas known collectively as the ventral stream. Damage to ventral stream areas may lead to visual agnosias that can severely compromise quality of life. It is therefore important to achieve an understanding of how shape representation is generated. We will examine the neural representation of shape in V4, a brain region that is situated at an intermediate level on the ventral stream hierarchy. Our stategy will be to construct quantitative models of the relationship between neurophysiological activity and visual input at both the single cell and population levels. Our approach to constructing these models will be distinguished by the use of advanced non-linear statistical techniques, complex visual stimuli that simulates natural viewing conditions, and the use of multi-electrode arrays to record populations of neurons simultaneously. Interpretation and analysis of these models will allow us adress two specific questions: 1) what are the independent stimulus dimensions to which V4 neurons are tuned?; 2) how is the distributed activity of V4 cell populations combined to represent shape? [unreadable] [unreadable] [unreadable]